1. Field of the Invention
The invention relates to a molding apparatus. In particular the invention relates to a mold closing device for fabricating machines for plastics by which at least one of the mold halves can be shifted between the open position and the closed position. After the mold halves are placed in the closed position, they are releaseably locked to each other.
2. Description of the Prior Art
In known mold closing devices, hydraulic cylinders are used to move the mold halves between their opened and closed positions. The hydraulic cylinders are positioned such that they engage the backs of plates on which the mold halves are mounted. Once the hydraulic cylinders move the mold halves to the closed position, the halves are locked up. This type of apparatus involves a central system of movement; that is, the power for locking the mold halves together has to be supplied by the same hydraulic cylinders which supply the moving power. Alternatively, some apparatus known in the art use mechanical devices to lock up the mold after it is closed. These mechanical devices usually act in the manner of toggle fasteners.
The locking force required to hold the mold closed varies depending upon the process being performed (i.e., blow molding or injection molding) and the specific product being fabricated. It is therefore necessary to use hydraulic cylinders designed to supply a variety of force magnitudes. In prior art apparatus, the same cylinders provide all the necessary movement forces, even though only relatively low forces are necessary for transporting the mold halves compared to the forces necessary for locking up the mold halves. In order to provide the forces necessary to lock up the mold halves, the hydraulic cylinders must butt against the frame of the mold apparatus. This limits the locations at which the cylinders can be mounted in on any one machine. When large mold holders or mounting plates are used, the hydraulic cylinders provide an irregular distribution of the locking forces and consequently varying deformations occur within the clamping plates. The same problems occur even when the locking forces from the hydraulic cylinders are transmitted directly to the mold halves. The high bending forces exerted by the cylinders against the beams of the machine body require that the free ends of the beams be coupled by a yoke. This coupling limits the space available for mold changing or product removal. What room there is existing within the frame of the apparatus is additionally limited by the presence of the large hydraulic cylinders within the space of the framework.
It is easily seen, therefore, that the prior art design results in an expensive, heavy machine with greatly oversized hydraulic apparatus and its attendant high consumption of hydraulic fluid. The fixed arrangement of cylinders causes an unfavorable pattern of force application and greatly restricts the space for mold installation. An apparatus that combines the mold transport and mold lock-up functions greatly restricts the applications of the plastic fabricating machine because there are limits to the size of the mold which can be used. This limitation is further aggravated by the need for the machine body to withstand the reaction forces of the compression cylinders.
In order to avoid the use of heavy or reinforced framework or beams, the deformation forces on the machine body must be eliminated while providing good distribution of the closing and locking forces over the mold halves. This should be done using a movement mechanism which is smaller and more powerful than those used in prior art devices in order to optimize the space within the plastic fabricating machine.